The invention relates to an injection device for a fuel reservoir injection system of an internal combustion engine.
Injection devices of this kind are sufficiently known from current use. Fuel reservoir injection systems, common rail injection systems for a multi-cylinder internal combustion engine have a high-pressure fuel distributor or rail from which a number of high-pressure fuel supply paths each lead to a respective injection nozzle that protrudes into one of the cylinder combustion chambers of the internal combustion engine.
The fuel injection into the respective combustion chamber is controlled by means of a nozzle needle, which opens and closes the injection nozzle as a function of the pressure in a control chamber. In order to build up pressure in the control chamber, a continuously open inlet conduit is provided, through which the fuel at rail pressure can flow from the respective fuel supply path into the control chamber. Fuel can the released from the control chamber by means of a separate outlet path and can thus bring about a pressure relief in the control chamber. Through intentional opening and closing of a shutoff valve disposed in the outlet path, influence can be exerted on the pressure level in the control chamber and therefore on the position of the nozzle needle.
If the valve is opened, fuel flows out of the control chamber. The attendant pressure drop in the control chamber causes the nozzle needle to lift up from a seat in the injection nozzle and fuel comes out of the injection nozzle. If the valve is closed again, the replenishing flow of fuel arriving via the inlet conduit causes the pressure in the control chamber to build back up again. As a result of this pressure increase, the nozzle needle is pressed against its seat again and closes the injection nozzle. The outlet path and the inlet conduit are embodied so that when the outlet path is open, the flow rate of the fuel flowing out via the outlet path is greater than the flow rate of the replenishing fuel arriving via the inlet conduit, effectively reducing the fuel volume in the control chamber.
The metering precision of the injected fuel quantity is essentially determined by the speed with which the injection nozzle can be opened and closed. In the closing of the nozzle, the comparatively small flow cross section of the inlet conduit can mean that there is not enough of a replenishing fuel flow to achieve sufficiently rapid closing times.
In order nevertheless to be able to compensate for the fuel losses sustained in the control chamber with sufficient speed, one strategy is to provide a bypass conduit that branches from the fuel supply path and feeds into the outlet path. If the shutoff valve is closed, an additional fuel flow can flow through this bypass conduit, out of the fuel supply path and into the control chamber by means of a part of the outlet path in the vicinity of the control chamber. It has turned out that this permits higher closing speeds of the nozzle needle to be achieved.
However, it has also turned out that the feeding of the bypass conduit into the outlet path can cause interference in the flow behavior of the fuel as it flows out of the control chamber. For example, inevitable flow edges at the infeed point can cause turbulence which end ups preventing the fuel quantity required to open the injection nozzle from flowing out of the control chamber with the desired speed. The delayed opening of the injection nozzle can then have disadvantageous effects on the metering precision.
According to the invention, the infeed point of the bypass conduit is disposed in the outlet path in the vicinity of the valve chamber. It has turned out that by locating the infeed point here, undesirable interference of the flow behavior of the fuel flowing out of the control chamber can be kept very slight. Since intensified turbulence of the fuel flow must as a rule be reckoned with anyway in the vicinity of the valve chamber, the additional turbulence effect of the flow edges of the infeed point is insignificant by comparison with this other turbulence.
If the bypass conduit is open, provided that there is a pressure difference, fuel flows from the fuel supply path, via the bypass conduit, into the outlet path, and increases the pressure there. Whereas this effect is desirable during the closing of the injection valve in order to fill the control chamber more rapidly, during the opening of the injection valve, the fuel flow being diverted into the outlet path via the bypass conduit can partially hinder the outflow of fuel from the control chamber to a significant degree and can thus lead to a delayed opening of the injection nozzle. The bypass conduit infeed point location according to the invention has also turned out to be advantageous in this regard.
In the vicinity of the valve chamber, there is sufficient freedom of structural design to permit the bypass conduit to feed into the outlet path so that such hindrances to the outflow of fuel can be kept to a minimum. The bypass conduit can therefore easily remain open all the time.
As a rule, an outlet throttle can be disposed in the outlet path, upstream of the valve chamber, and this outlet throttle can be used to set a desired flow of the outflowing fuel. This outlet throttle is preferably spaced apart from the valve chamber along the outlet path.
It is turned out that the embodiment of the region of the outlet path between the outlet throttle and the valve chamber can be of decisive importance to the flow behavior of the outflowing fuel. In particular, through suitable embodiment of his region of the outlet path, cavitation can be produced in the outlet throttle when fuel flows out of the control chamber. Cavitation in the outlet throttle has the advantage that the flow through the outlet throttle is independent of the pressure in the valve chamber and therefore independent of a possible fuel influx via the bypass conduit.
Since according to the invention, the bypass conduit feeds into the valve chamber and the region of the outlet path between the outlet throttle and the valve chamber is consequently free of flow edges, which can be produced by the infeed of the bypass conduit, this region of the outlet path can be more easily optimized design-wise with regard to a desired flow behavior in the fuel outflow than would be the case if the bypass conduit were to feed into the outlet path between the outlet throttle and the valve chamber.
A preferred embodiment of the invention provides that the shutoff element be embodied as a seat element that can be moved in the valve chamber between two opposing valve seats, that the upstream and the downstream sections of the outlet path feed into the valve chamber at the two valve seats, and that the infeed point of the bypass conduit into the valve chamberxe2x80x94with regard to the outflow direction of the fuelxe2x80x94is disposed between the two valve seats.
It goes without saying, though, that an embodiment of the shutoff valve as a piston slide valve or as a single-seat valve is in no way excluded from the scope of the invention.
Other advantages and advantageous embodiments of the subject of the invention can be inferred from the specification, the drawings, and the claims.
An exemplary embodiment of the invention will be explained in detail below in conjunction with the accompanying drawings.